A publishing company! It would be a dream to have a publishing company (all the books...) Or an apparel company.
I've always had the idea of having a company that is widespread, inexpensive, and supplies cosplay clothing, clothing inspired by anime, and shirts with cool designs on them. Kinda like Target. I don't see why it hasn't been done - I reckon there are enough fans to make it sucessful. Taking into consideration all the ugly designs the designer labels come out with, I reckon it'd be a hit even with people who don't like anime.